Direct imaging type SIMS instrument

Abstract

There is disclosed a direct imaging type SIMS (secondary ion mass spectrometry) instrument having a mass analyzer comprising superimposed fields. The superimposed fields consist of a toroidal electric field and a uniform magnetic field substantially perpendicular to the electric field. In said electric field, the central orbit of the ion beam is located in an equipotential plane. The mass analyzer causes an image of the region on the sample bombarded with a primary beam to be focused onto a two-dimensional detector to form a mass-filtered ion image. The SIMS instrument can operate in a mode where only the intensity of the magnetic field of the mass analyzer is set equal to zero. In this mode, only ions having a selected energy within a certain energy bandwidth produce an image, that is, an energy-filtered ion image is formed.

What is claimed is: 
     
       1. A direct imaging type SIMS instrument comprising: a beam source for producing and directing a primary beam toward a sample position to cause emanation of secondary ions from a sample at said position;   a mass analyzer into which are introduced secondary ions emanating from a sample at the sample position by the bombardment of the primary beam, the mass analyzer comprising a magnetic field and an electric field superimposed on the magnetic field, the electric field being perpendicular to the magnetic field wherein secondary ions entering the mass analyzer are caused to traverse a circular orbit, one selected orbit being the central ion orbit, said magnetic field being generated by an exciting coil wrapped around a yoke terminating in two facing pole pieces having substantially flat and parallel facing surfaces on each side of the central ion orbit and said electric field being generated by applying electrical potentials to a plurality of concentric electrodes attached to surfaces of insulating base plates positioned substantially parallel to the facing surfaces of the magnetic pole pieces,   a two-dimensional detector disposed on the output side of the mass analyzer for displaying an image of the bombarded region on the sample focused onto the detector, and   means for switching between at least two modes, a first mode wherein the electric and magnetic fields are so balanced to produce a mass-filtered ion image at the two-dimensional detector and a second mode wherein the intensity of the magnetic field is set to zero and the intensity of the electric field is adjusted to produce an energy filtered image at the two-dimensional detector.   
     
     
       2. A direct imaging type SIMS instrument comprising: a beam source for producing and directing a primary beam toward a sample position to cause emanation of secondary ions from a sample at said position;   a mass analyzer into which are introduced secondary ions emanating from a sample at the sample position by the bombardment of the primary beam, the mass analyzer comprising a magnetic field and an electric field superimposed on the magnetic field, the electric field being perpendicular to the magnetic field wherein secondary ions entering the mass analyzer are caused to traverse a circular orbit, one selected orbit being the central ion orbit having radius a,   a two-dimensional detector disposed on the output side of the mass analyzer for displaying an image of the bombarded region on the sample focused onto the detector,   means for switching between at least two modes, a first mass-filtered ion image mode wherein the electric and magnetic fields the intensity of the magnetic field and the intensity of the electric field are set such that   a/a.sub.m =2 and a/a.sub.e =-1        where a m  is the ion path radius due to the magnetic field alone and a e  is the ion path radius due to the electric field alone and the electric field is distributed so that a/Re=-1 wherein Re is the radius of curvature of the intersection of a plane and the equipotential surface through the central ion orbit wherein said plane passes through the center of curvature and is perpendicular to the plane of the central ion orbit, and   an energy-filtered ion image mode wherein the magnetic field is set equal to zero such that a/a m  =- and the electric field is produced such that a/a e  =1 and the intensity of the electric field is the same as in the mass-filtered image mode.